This invention relates generally to the monitoring and evaluation of interface bonding between different material layers and more particularly to the determination of bonding integrity at interfaces between an acoustical radiation transmissive material such as metal and a radiation attenuating material such as an elastomer.
The concept of generating and applying pulsed radiation to bonded materials to determine adhesion integrity by measurement of response signal amplitude of reflected radiation is already known, as disclosed for example in U.S. Pat. No. 3,605,486 to Anderholm et al. According to the Anderholm et al patent, stress pressure waves induced by the pulsed radiation internally of the bonded materials partially cancel each other to affect the reflected response signal picked up for bonding evaluation. However, such evaluation involves incrementally increasing the amplitude of the stress pressure waves induced until bond failure is achieved in order to determine bond quality by measurement of the maximum signal amplitude
Various signal processing techniques associated with systems for testing and evaluating ultrasonic acoustical materials are disclosed in U.S. Pat. No. 4,088,028 to Hildebrandt and U.S. Pat. Nos. 4,274,828, 4,755,953, 4,799,168 and 4,803,638. Partial signal phase cancellation and logarithmic scaling techniques are furthermore respectively referred to in U.S. Pat. Nos. 4,274,288 and 4,755,953 to Tittman et al. and Geithman et al. The technique of gating echo pulses by means of acceptance time windows is disclosed in each of U.S. Pat. Nos. 4,799,168 and 4,803638 to Sarr and Nottingham et al, respectively. However, the signal processing techniques disclosed in the latter referred to patents are not associated with the evaluation of bonding integrity.
Time delay spectrometers of the acoustical type are generally known in the art as disclosed in U.S. Pat. Nos. 3,466,652 and 4,279,019 to Heyser, as well as associated signal processing techniques. However, such spectrometer arrangements, because of time/frequency measurement limitations, are not satisfactory for use in measuring and evaluating the effects of interface bonding integrity on acoustic resonance.
It is therefore an important object of the present invention to provide a new and useful pulse echo type of material inspection system for reliably determining interface bonding integrity without destruction of the bonding so as to have widespread commercial applications as well as for critical explosive/propellant purposes in warheads and rocket motors.